As an example of the mobile communication system applicable to the present invention, a 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) communication system will hereinafter be described in detail.
FIG. 1 shows an Evolved Universal Mobile Telecommunications System (E-UMTS) network structure serving as an example of a mobile communication system.
The E-UMTS system is an evolved version of the conventional Universal Mobile Telecommunications System (UMTS) system and basic standardization thereof is in progress under the 3rd Generation Partnership Project (3GPP). Generally, the E-UMTS is also referred to as a Long Term Evolution (LTE) system.
The E-UMTS network may be classified into an Evolved-UMTS Terrestrial Radio Access Network (E-UTRAN) 101 and a Core Network (CN) 102. The E-UTRAN includes a UE 103, a BS (eNB or eNode B) 104a, . . . , 104n, and an Access Gateway (AG) 105 which is located at an end of a network and is connected to an external network. The AG 105 can be divided into a part that handles processing of user traffic and a part that handles control traffic. Here, the AG part for processing new user traffic and the AG part for processing control traffic can communicate with each other using a new interface.
One or more cells may exist for one eNB. An interface for transmitting user traffic or control traffic can be used between eNBs. A Core Network (CN) 102 may include the AG 105 and a node or the like for user registration of the UE 103. An interface for discriminating between the E-UTRAN 101 and the CN 102 may be used.
Radio interface protocol layers between the UE and the network can be classified into an L1 layer (first layer), an L2 layer (second layer) and an L3 layer (third layer) on the basis of the lower three layers of the Open System Interconnection (OSI) reference model widely known in communication systems. A physical layer belonging to the L1 layer provides an information transfer service utilizing a physical channel. A Radio Resource Control (RRC) layer located at the L3 layer controls radio resources between the UE and the network. For this operation, RRC messages are exchanged between the UE and the network via the RRC layers. The RRC layers may be distributed among base stations (BSs) (104a, . . . , 104n) and network nodes, or may be located only at base stations (BSs) (104a, . . . , 104n) or the AG 105.
FIG. 2 and FIG. 3 illustrate radio interface protocol structures between a UE and a UTRAN that are based on a 3GPP radio access network standard.
The radio interface protocol of FIG. 2 or FIG. 3 is divided horizontally into a physical layer, a data link layer and a network layer, and vertically into a user plane for transmitting data information and a control plane for transmitting a control signal such as a signaling message. In more detail, FIG. 2 shows individual layers of a radio protocol control plane and FIG. 3 shows individual layers of a radio protocol user plane. Protocol layers of FIGS. 2 and 3 can be classified into an L1 layer (first layer), an L2 layer (second layer) and an L3 layer (third layer) on the basis of the lower three layers of the OSI reference model widely known in communication systems.
The following is a detailed description of respective layers of the radio protocol control plane of FIG. 2 and the radio protocol user plane of FIG. 3.
The physical layer, which is the first layer, provides an information transfer service to an upper layer using a physical channel. The physical layer (PHY) is connected to a Medium Access Control (MAC) layer, located above the physical layer, through a transport channel. Data is transferred between the MAC layer and the physical layer through the transport channel. In this case, the transport channel is classified into a dedicated transport channel and a common transport channel according to whether or not a channel is shared. Data transfer between different physical layers, specifically between the respective physical layers of a transmitter and a receiver, is performed through the physical channel.
A variety of layers exist in the second layer (L2 layer). The MAC layer maps various logical channels to various transport channels, and performs logical-channel multiplexing for mapping various logical channels to one transport channel. The MAC layer is connected to the RLC layer serving as an upper layer through a logical channel. The logical channel can be classified into a control channel for transmitting information of a control plane and a traffic channel for transmitting information of a user plane according to categories of transmission information.
The RLC layer of the second layer performs segmentation and concatenation on data received from an upper layer, and adjusts the size of data to be suitable for a lower layer transmitting data to a radio interval. In order to guarantee various Qualities of Service (QoSs) requested by respective radio bearers (RBs), three operation modes, i.e., a Transparent Mode (TM), an Unacknowledged Mode (UM), and an Acknowledged Mode (AM), are provided. Specifically, an AM RLC performs a retransmission function using an Automatic Repeat and Request (ARQ) function so as to implement reliable data transmission.
A Packet Data Convergence Protocol (PDCP) layer of the second layer (L2) performs a header compression function to reduce the size of an IP packet header having relatively large and unnecessary control information in order to efficiently transmit IP packets such as IPv4 or IPv6 packets in a radio interval with a narrow bandwidth. As a result, only information required for a header part of data can be transmitted, so that transmission efficiency of the radio interval can be increased. In addition, in the LTE system, the PDCP layer performs a security function, this security function is composed of a ciphering function for preventing a third party from eavesdropping on data and an integrity protection function for preventing a third party from handling data.
A Radio Resource Control (RRC) layer located at the top of the third layer (L3) is defined only in the control plane and is responsible for control of logical, transport, and physical channels in association with configuration, re-configuration and release of Radio Bearers (RBs). The RB is a logical path that the first and second layers (L1 and L2) provide for data communication between the UE and the UTRAN. Generally, Radio Bearer (RB) configuration means that a radio protocol layer needed for providing a specific service, and channel characteristics are defined and their detailed parameters and operation methods are configured. The Radio Bearer (RB) is classified into a Signaling RB (SRB) and a Data RB (DRB). The SRB is used as a transmission passage of RRC messages in the C-plane, and the DRB is used as a transmission passage of user data in the U-plane.
A downlink transport channel for transmitting data from the network to the UE may be classified into a Broadcast Channel (BCH) for transmitting system information and a downlink Shared Channel (SCH) for transmitting user traffic or control messages. Traffic or control messages of a downlink multicast or broadcast service may be transmitted through a downlink SCH and may also be transmitted through a downlink multicast channel (MCH). Uplink transport channels for transmission of data from the UE to the network include a Random Access Channel (RACH) for transmission of initial control messages and an uplink shared channel (SCH) for transmission of user traffic or control messages.
Downlink physical channels for transmitting information transferred to a downlink transport channel to a radio interval between the UE and the network are classified into a Physical Broadcast Channel (PBCH) for transmitting BCH information, a Physical Multicast Channel (PMCH) for transmitting MCH information, a Physical Downlink Shared Channel (PDSCH) for transmitting downlink SCH information, and a Physical Downlink Control Channel (PDCCH) (also called a DL L1/L2 control channel) for transmitting control information, such as DL/UL Scheduling Grant information, received from first and second layers (L1 and L2). In the meantime, uplink physical channels for transmitting information transferred to an uplink transport channel to a radio interval between the UE and the network are classified into a Physical Uplink Shared Channel (PUSCH) for transmitting uplink SCH information, a Physical Random Access Channel for transmitting RACH information, and a Physical Uplink Control Channel (PUCCH) for transmitting control information, such as HARQ ACK or NACK Scheduling Request (SR) and Channel Quality Indicator (CQI) report information, received from first and second layers (L1 and L2).